As result of aging, disease and/or injury, the non-bony tissues disposed between adjacent bone structures can lose their resilience and shock absorbing characteristics which may result in pain and decreased range of movement in the affected area. For example, consider degenerative disc disease of the spine. The human spine is formed by an arranged column of bone structures (vertebra) separated by small cartilaginous cushions identified as intervertebral discs designed to absorb pressure (axial load) and keep the spine flexible. The disc contains a jelly-like nucleus pulposus surrounded by an outer ring of tough elastic ligament material that holds the vertebrae together, called the annulus fibrosus. As the disc degenerates, the nucleus and annulus becomes thinner and less able to handle axial loads. The annulus may begin to bulge (disc herniation) or rupture, narrowing the intervertebral disc space and impinging nerves within or adjacent to the spinal column, which may result in the individual experiencing pain of varying degree and manifestation, diminished flexibility, and reduced range of motion.
In order to reduce the pain associated with the movement of the intervertebral joint, surgical intervention is often indicated as a means to alleviate pressure upon the spinal cord while concomitantly stabilizing the associated vertebrae. This involves a surgical procedure to distract the disc, vertebra, or portions thereof, and insert intervertebral implants into the cavity created between the opposing vertebra to help support the spine and restore the normal spacing.
The most commonly used intervertebral devices are substantially rigid and manufactured at various preset heights requiring a cavity between opposing vertebrae be prepared and distracted to a dimension corresponding to the most suitably sized device. Some of these implants are hollow so that they may be packed with osteogenic material to ensure solid bone growth through and around the implant, fusing the two vertebrae. The surgical procedure to prepare the implant site can be difficult and lengthy. Moreover, the procedure requires the surgeon to create large incisions and passageways to the targeted disc space, resulting in increased recovery time, pain, and risk of trauma to the tissues surrounding the implant site.
Recently, expandable implants have been developed that may be used as both a fusion device and/or a means for maintaining intervertebral spacing. Often these implants are in the form of an expandable hollow cavity (balloon, bladder) in fluid communication with a fluid delivery means. The collapsed balloon is capable of being positioned within a disc cavity and expanded in situ by the introduction of fluid (gas, liquid) until the balloon is inflated to a size that corresponds to the cavity created when the damaged tissue is removed. The fluid delivery means typically includes a pressure monitoring component (e.g., pressure gauge, pressure sensor) used to determine when the balloon has reached the necessary size within the disc space. During the filling process, these types of systems must be carefully controlled lest the expanded balloon reaches a size or applies pressure in an amount that will overextend the disc cavity, creating additional injury to the surrounding tissue and/or bony surfaces.